Soldering is a complex task that requires much precision on the part of the operator. With enough practice, one can gain a better understanding of the tools and techniques, thereby improving productivity and quality and decreasing the risk of board damage. Discussed in this blog are some of the basics of hand soldering—note that this blog is not a substitute for hands-on practice.
First, strict process controls must be developed, ensuring the consistency and repeatability of your results.
The second major component to successful hand soldering is tip selection. It is important to choose the correct geometry for application such that the tip fits the joint correctly, resulting in greater power delivery, increased tip life, and higher efficiency. Using a tip that is too small will take longer, abuse the tip, and not efficiently pass power to the load. On the other hand, a tip that is too large will abuse the tip, damage the PCB, and cause a hole in the tip. Shorter, bulkier tips deliver more power. Short, blunt tips should only be used for heavy loads. Long, fine tips are best for hard-to-reach applications or fine terminals, but note that they don’t deliver power as efficiently, since the joint is so far from the heater. Another thing to note is that larger tips generally have more iron plating, which makes them more robust in abrasive conditions.
The next thing to consider is temperature selection. Try to use the lowest temperature possible, as this reduces the risk of damage to the board. To change temperature, you have to change the tip cartridge.
Finally, you want to consider flux selection. Clean (RMA) flux is the most traditional flux and is high in acidity. No-clean flux is the most common. In no-clean, there is less flux per volume in the wire core solder. No-clean has weaker acidity than RMA. When working with no-clean flux, you need to work with lower temperatures. Aqueous (OA) flux has inorganic acid that is more active than that of RMA flux. RMA flux leaves more residue that needs to be cleaned off the PCB, while no-clean flux requires less cleanup. However, RMA is better than no-clean for the tip.
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Sloan, David & Huerta, Leo. Hand Soldering Basics. Metcal.